A complete life cycle or metamorphosis is the type of insect development that has four distinct stages: egg, larva, pupa, and adult. Insects with this development include mosquitoes, wasps, flies, beetles, green lacewings, and ladybugs. An incomplete life cycle is a gradual metamorphosis. It is a type of insect development with no prolonged resting or pupal stage. The three stages are egg, nymph, and adult. Insects with this type metamorphosis include silverfish and the true bugs like stink bugs, boxelder bugs, minute pirate bugs, and squash bugs. Instars are the immature forms of incomplete insects.

Some animals we call insects really aren't. These insectlike critters include spiders, mites, and galls. Galls aren't even animals; they are plant growths that are caused by fungi or insects. Insect galls are the most common. Mites and spiders are different from insects in that they have eight legs instead of six. These critters are included in the book because they are so similar and because of their economic importance and influence on the balance of life.